1. Field of the Invention
The present invention relates generally to a radiation monitor and, more particular, to a radiation monitor including an electrometer exhibiting relatively low leakage over a range of temperatures.
2. Discussion of the Prior Art
Radiation monitors are commonly deployed in a location proximate to known radiation sources, such as nuclear power generation stations, to monitor radiation levels. In response to the detection of radiation, radiation monitors will produce a current that is proportional to the quantity of radiation detected. Radiation monitors often use electrometers to convert this relatively low current into a voltage signal for processing.
As part of electrometer arrangements, switches are employed to provide an ability of resetting (i.e., discharging) associated capacitors. It is possible use electronic switches such as Field effect transistor (FET) switch devices. Some specific FET devices such as MOSFET and JFET could be used. Also, is possible to use electromechanical switches such as reed relay devices.
A FET device can be susceptible to current leakage. The amount of current leakage can vary with temperature variation. Specifically, increasing temperature will cause a greater amount of leakage. For example it is possible for the amount of leakage to double for each increase of 10° Celsius in temperature. As such, over a relatively wide temperature range, a FET could have a greatly changing amount of current leakage. Also, such current leakage could begin at temperatures as low as 35° Celsius. Current leakages can be problematic, as they adversely affect the accuracy of radiation detection.
In one effort to avoid the problem of current leakage, the electromechanical switches such as the reed relay devices could be used. However, these reed relay devices are relatively bulky/large in size and have a slow switching speed.
Issues concerning temperature-based leakage variation and/or bulkiness/slowness may not be sufficiently problematic is some uses of electrometer arrangements. However, there are some scenarios in which these issues would be problematic. An electrometer within radiation monitor would be such a scenario. Radiation monitors could be exposed to environmental temperatures that could rise to 50-60° Celsius. Accordingly, it would be beneficial to provide a radiation monitor with an electrometer that exhibits relatively low leakage rates over a wide range of temperatures without the bulk of a reed relay device.